[en] For miniaturized capacitive energy storage, volumetric and areal capacitances are more important metrics than gravimetric ones because of the constraints imposed by device volume and chip area. Typically used in commercial supercapacitors, porous carbons, although they provide a stable and reliable performance, lack volumetric performance because of their inherently low density and moderate capacitances. In this paper, we report a high-performing electrode based on conductive hexaaminobenzene (HAB)-derived two-dimensional metal-organic frameworks (MOFs). In addition to possessing a high packing density and hierarchical porous structure, these MOFs also exhibit excellent chemical stability in both acidic and basic aqueous solutions, which is in sharp contrast to conventional MOFs. Submillimetre-thick pellets of HAB MOFs showed high volumetric capacitances up to 760 F cm^-3 and high areal capacitances over 20 F cm^-2. Furthermore, the HAB MOF electrodes exhibited highly reversible redox behaviours and good cycling stability with a capacitance retention of 90% after 12,000 cycles. In conclusion, these promising results demonstrate the potential of using redox-active conductive MOFs in energy-storage applications.

[en] NiCo₂O₄ directly grown on nickel foam was fabricated via a simple hydrothermal method in glycol solution with different volume ratios of water to glycol with the aim to control the shape of as-prepared products. It was found that NiCo₂O₄ shape strongly depends on glycol content in reaction solution. As 1:0, 1:1, 1:2 and 1:3 volume ratios of water to glycol were selected, the corresponding NiCo₂O₄ exhibited 3D hierarchical honeycombs composed of numerous nanorods, 1D nanoneedles, 2D interconnected nanosheets and ultrathin nanosheets with numerous micropores, respectively. The morphology of NiCo₂O₄ has remarkable influence on electrochemical performance. The NiCo₂O₄ nanoneedles with open mesoporous structure and ultrathin nanosheets with numerous micropores displayed superior electrochemical properties than other products. The specific capacitances of NiCo₂O₄ nanoneedles and nanosheets can reach 708 and 634 F g⁻¹ at current density of 1 A g⁻¹, respectively. Rate capabilities 88.7% and 92.9% and cycling performance of 86.5% and 88% capacitance retentions at 5 A g⁻¹ after 2000 cycles were obtained. These outstanding results are ascribed to their structure advantages, i.e. open mesoporous feature, numerous electroactive surface sites and excellent conductivity, guaranteeing short ions diffusion path and fast faradic reaction rate. (paper)

[en] Highlights: • Successful synthesis of poly(vinyl alcohol), PVA, and graphene oxide composite. • Improvement of conductivity of poly(vinyl alcohol) with reduced graphene oxide. • Improvement of electrochemical properties of PVA with reduced graphene oxide. Poly(vinyl alcohol), PVA, polymer was successfully combined with graphene oxide (GO) and thermally reduced graphene oxide (RGO), respectively, to make composites and characterized for supercapacitor applications. PVA-RGO composite shows excellent electrochemical properties compared to PVA-GO composite. The capacitance of 190 Fg⁻¹ is obtained from PVA-RGO composite which is larger than that (13 Fg⁻¹) of PVA-GO composite. Electrochemical impedance of PVA-RGO is more than ten times smaller than that of PVA-GO at 20 kHz, demonstrating that PVA-RGO composite has a great advantage for supercapacitor applications compared to PVA, GO, RGO, and PVA-GO composite.

[en] Flexible supercapacitors with electrodes coated on inexpensive fabrics by the dipping technique. This paper present details of the design, fabrication and characterisation of fabric supercapacitor. The sandwich structured supercapacitors can achieve specific capacitances of 11.1F/g, area capacitance 105 mF.cm⁻² and maintain 95% of the initial capacitance after cycling the device for more than 15000 times

[en] Highlights: • Ni_xP nanowires/Ni hybrid foam is obtained by a facile and large-scale method. • Supercapacitor performance for Ni_xP nanowires/Ni hybrid foam is investigated. • Ultrahigh rate performance is observed for Ni_xP nanowires/Ni hybrid foam. • Ni_xP nanowires/Ni hybrid foam shows long-term cycling stability.

[en] PIn/MoS₂ composite prepared via in-situ oxidative polymerization of indole monomer in the presence of exfoliated MoS₂ sheets shows fair capacitive performance. The specific capacitance reaches a value of 173 F g^-1 at the current density of 1 A g^-1. The close integration of PIn and MOS₂ generating interfaces involving two different materials leads to enhanced charge storage properties in the composite. The composite stores charge in bulk mainly through pseudocapacitive mechanism along with some surface storage. The presence of micro and mesopores enhances the surface area and also facilitates the easy charge transport through the electrode material. The composite also shows excellent cyclic stability due to the presence of stable MoS₂. (author)

[en] Highlights: • The performances degradation of supercapacitors during power cycling ageing tests have been quantified. • The performances recovery phenomena of supercapacitors is highlighted and modelled. • The impact of the rest conditions (temperature and cut-off voltage) on the recovery behaviour is quantified. • An accurate ageing model able to predict the performances degradation of supercapacitors in power cycling is proposed. - Abstract: During accelerated ageing tests of supercapacitors (SC), a decay in their performance is reflected by a decrease in capacitance and an increase in equivalent series resistance ESR. In power cycling, when electric solicitations of the SC are interrupted for the purposes of real use or characterisation, performance recovery is observed, mainly in terms of an increase in capacitance. This phenomenon is due to a redistribution of electrical charges, balancing of impurities inside the porous carbon electrodes, and the cell’s return to thermodynamically steady-state conditions. A repetitive long rest period during cycling appears to slow down the ageing process, and to reduce the decay in performance. The impacts on capacitance recovery during rest time, of both cut-off voltage and temperature, are studied. A nonlinear analytical expression is used to predict the capacitance decay for several durations and test interruption periodicities; this is also used to model the capacitance during rest time, taking the cut-off voltage, rest time and temperature into account

[en] Acta MaterialiaVolume 152, 15 June 2018, Page 300

[en] Nickel molybdate (NiMoO₄) nanoparticles (NPs) are prepared by different synthetic techniques via hydrothermal (SHC), gel-combustion (SGC) and microwave-assisted combustion (SMC) methods. All prepared samples are subjected to calcination at 600 °C to get a pure α-NiMoO₄ with a monoclinic crystal structure and their physico-chemical properties are compared. The average crystallite size of SMC is smaller than that of other two methods. Depending on the synthetic process, NiMoO₄ NP_s exhibits different morphology. Optical band gap energies for all samples are calculated. The cyclic voltammograms signify the occurrence of redox couples and besides with the electrochemical impedance spectra (Nyquist plot) confirm the supercapacitive nature. Among all, the modified SMC electrode material deliver highest specific capacitance value related with scan rate and current density. Nevertheless, SMC exhibits lowest faradic resistance and also grants well permanency with a stable profile of 98.6% retentivity after 1000 cycles results in high electric activity.

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